When a hoisting accessory (generally referred to as a spreader) is landed on a container in order to hold a container stowed on the ground by a cargo crane such as a bridge crane for container yard, or when a container is stacked (including a time when a container is stowed on a specified position on the ground), it is necessary to adjust positions of the hoisting accessory or the container held by the hoisting accessory with respect to the container stowed on the ground or with respect to a specified position on the ground in predetermined accuracy. Particularly in the instance of stacking the container, it is necessary to stack the container so that horizontal displacement does not occur in the upper and lower containers.
In order to perform such operation, it is necessary to detect the specified position on the ground where the container is to be stowed, or the relative position of the container on the ground which is an object to be held by the hoisting accessory, or an object which a container held by the hoisting accessory is stacked thereon (in the explanation below, the specified position on the ground and the container on the ground to be held or stacked is referred to as an “target container”) and the hoisting accessory or a container held by the hoisting accessory (in the explanation below, referred to as a “suspended container”), and it should be controlled so that there is no displacement in the relative position.
Explanation below is given, assuming that an operation of stacking a container held by a hoisting accessory on a container stowed on the ground, unless otherwise specified. However, it is a matter of course that the similar technique can be applied to the operation for landing the hoisting accessory on a container stowed on the ground or the operation for stowing a container held by the hoisting accessory on a specified position on the ground. In the explanation below, explanation about edge detection of the suspended container is also applicable to the edge detection of the hoisting accessory itself, unless otherwise specified, and explanation about the edge detection of a target container is also applicable to the edge detection of a target mark which is installed on the ground to facilitate loading in the first stage, unless otherwise specified.
As the conventional technology for detecting a position of a target container in the cargo crane, there are known one in which a distance between a hoisting accessory and a side of a container is measured by a ultrasound horizontal distance detector fitted to the hoisting accessory, so that the position of the target container is detected from the measurement, as disclosed in Japanese Patent Application Laid-Open No. 5-170391 (Patent No. 2831190), and one in which a picture of the lower part of the hoisting accessory is taken by an image pickup unit such as a CCD camera fitted to the hoisting accessory, and an edge of a target container is found by an image processing technique from the image data thereof, and the position of the target container is detected based on this finding.
In European Patent Application No. 0440915A1, there is disclosed a technique in which a corner of a target container connected to a hoisting accessory is imaged by an image pickup unit such as a CCD camera fitted downwards to the hoisting accessory, the relative position between the hoisting accessory and the target container is then detected by the image processing technique, thereby positioning at the time of connecting the container to the hoisting accessory is automatically performed by position control of the hoisting accessory based on the relative position.
The one which measures the distance between the hoisting accessory and the container side face by the horizontal distance detector has a problem of interference between the horizontal distance detector and the container. When it is tried to position the horizontal distance detector at a measurement position, at a stage where the horizontal displacement between the target container and the suspended container is large, there is the possibility that the horizontal distance detector collides with the target container, and hence it is difficult to actually put it to a practical use.
The one which picks up an image of the lower part of the hoisting accessory by the image pickup unit such as a CCD camera, and extracts the edge of the target container by the image processing technique from the obtained image data does not have the possibility of interference and collision, but has a problem in processing the image data picked up by the CCD camera or the like in the environment of the actual crane operation, to thereby extract the target container without any error. In the actual operating environment, influences of a change in the weather condition, a change in the intensity of sunlight, or shadows caused by the crane itself, the suspended container or the adjacent container stack, as well as nonuniformity of the container painting or a difference in reflectivity on the surface of the container affect the operating environment. Therefore, practical extraction of the target container cannot be realized without eliminating these influences.
This invention has been proposed in order to solve the problems related to the edge detection of the target container by the image data processing of the image pickup unit such as CCD cameras, which occur due to the influences of the environmental conditions under the actual operation and the conditions of the target container. It is an object of the present invention to provide a container position detection method in a cargo crane which promotes operation automation of the cargo crane, by reliably and positively performing edge detection of the target container by processing the image data obtained by the image pickup unit such as a CCD camera installed in a hoisting accessory, while eliminating the influences of various situations and conditions in the actual operating environment, and by using the edge detection result to accurately and positively perform the detection of the relative position between the target container and the suspended container, and a container position detection apparatus which is used for executing the method, or a container landing/stacking control method.